<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" onload="boom();">

<rect id="r"/><use id="u" xlink:href="#r"><rect id="r"/></use>

<script type="text/javascript">

function boom()
{
  var r1 = document.getElementsByTagName("rect")[0]; // the first node with id="r" 
  var use = document.getElementById("u");
  document.documentElement.insertBefore(use, r1);
  r1.appendChild(use);
}

</script>

</svg>
